The invention relates to an arc extinguishing chamber of a low-voltage, high-current circuit breaker. For such circuit breakers, a particular difficulty is encountered when a current is required to be broken in a relatively high voltage, about 600 Volts rms single-phase or 1000 Volts rms three-phase, with a fairly low intensity of about 5 to 10 times the rated current of the circuit breaker.
The document EP 0,306,382 describes a multipole circuit breaker with a molded insulating case meeting this requirement, housing an operating mechanism coupled to a switching bar so as to perform opening and closing of all the poles of the circuit breaker. Each pole comprises a stationary contact means, a movable contact means and an arc extinguishing chamber. The stationary contact means comprise a fixed conducting current input strip supported by the back-plate of the case, stationary main contacts and a stationary arcing contact. The movable contact means comprise a fixed conducting current input strip also supported by the back-plate of the case, and a contact system having a plurality of identical main contacts arranged in two series of the same number on each side of a movable arcing contact extending longitudinally along the center axis of the pole, the length of the movable arcing contact being greater than the length of the movable main contacts. The arc extinguishing chamber is arranged above the first strip and comprises a stack of separators formed by metal arc deionization plates, each plate having a V-shaped notch. A pair of arcing horns, one lower and one upper, are located on each side of the stack of plates of the extinguishing chamber. The lower arcing horn is fixedly secured to the top face of the first strip, with an insulating shield arranged between these two elements, by means of three screws which ensure flow of the current between the arcing horn and the strip. The three screws are arranged at the apexes of an isosceles triangle, one of the screws being arranged along the center axis of the pole near to an edge of the insulating shield and of a wall for outlet of the breaking gases to the outside, and the other two screws being located near to the stationary main contacts. The width of the lower arcing horn decreases in the direction of migration of the arc towards the center screw, and the other two screws are located on each side of the stationary arcing contact and near to the corresponding stationary main contacts. When opening of the contacts takes place, the arc arises in the arcing contact separation zone situated along the center axis of the pole and subsequently develops in the center zone of the chamber. The arc migrates to the center screw which stabilizes the arc root. At the end of opening travel, the distance between the arcing contacts becomes greater than the distance between the main contacts, causing a new breakdown of the arc at the level of the main contacts on one of the sides of the chamber. The arc then develops on a second different path along one of the sides of the chamber, recentering progressively and encountering along its path cold surfaces where efficient absorption fostering extinguishing of the arc takes place.
In such a device, a large part of the chamber is used for extinguishing the arc. However, it is observed that one of the sides of the chamber remains largely unused, as after breakdown of the arc, the arc only develops on one of the sides of the chamber. The depth of the chamber, i.e. its longitudinal dimension between the entrance of the chamber and the gas outlet wall, must be sufficient to cope with the volume of energy exchange necessary for arc extinguishing. It is however desirable, for a circuit breaker of given performances, that the depth of the chamber be reduced, while keeping the same width, which is a dimension imposed in practice by fitters' standards of user.
The document FR 2,604,026 furthermore describes a circuit breaker wherein the lower arcing horn broadens out from its front part near the contacts to its rear part near the back-plate of the arc extinguishing chamber. The broadened rear part constitutes a collecting part of smaller surface than the cross-section of an arc root for an arc formed with a constant electrical current density corresponding to the rated breakdown current. The objective here is to direct the arc onto the collecting part and to stabilize it there. The stabilized arc then develops essentially in the center part of the chamber. Such a configuration is only efficient if the longitudinal dimension of the chamber, i.e. its depth between the stationary contact zone and the rear wall of the chamber performing removal of the gases is large. The width of the chamber can be reduced as it is not used for arc extinguishing.